In recent years, conductive resin compositions that are made from thermoplastic resins (such as polyamide resins) filled with conductive material (such as carbon blacks) has been commonly used for, for example, packing material for IC chips, and used in automobile parts aiming at electrostatic discharge prevention because of its excellent physical strength and abrasion resistance and cheap production cost.
However, depending on types of conductive material, adding conductive material may degrade the mechanical property and formability of such thermoplastic resins. For example, when the conductive material is a carbon black, the property of the carbon black will degrade the flexibility and formability of a complexed conductive resin composition, and furthermore, because of non-uniformity of carbon black dispersion, sufficient conductivity will not be obtained in a compact of the resin composition. Additionally, when the composition is filled with a large amount of carbon black, the kneadability/manufacturability of the composition will be significantly degraded.
Especially when the thermoplastic resin is a polyamide resin, a high load will be generated during kneading that polyamide resin to mix with carbon black, and carbon gel will be generated, causing insufficient dispersion during a forming process.
In order to solve such problems, many methods have been proposed. For example, Patent Literature 1 proposes a conductive resin composition that contains a polyamide resin, which is composed of a carbon black and plasticizers such as a sulfonamide derivative. Moreover, Patent Literature 2 proposes a conductive resin composition that contains a polyamide resin, which is mixed with a carbon black and ester compounds such as a polyglycerine ester. Furthermore, Patent Literature 3 proposes a conductive resin composition that contains a polyamide resin, which is mixed with a carbon black and a carboxylic acid or an anhydride thereof.
However, the content of such carbon blacks in those conductive resin compositions still needs to be small because a large content thereof will significantly degrade the kneadability/manufacturability of the compositions.
In recent years, carbon nanotubes, which can be used as a conductive material in a similar way to carbon blacks, have been newly developed and application thereof has been examined. For example, Patent Literature 4 and 5 propose complex materials, in which resins of the materials contain carbon nanotubes that are 3.5 nm to 70 nm long in diameter and have lengths 5 or more times as long as their diameters, and production methods thereof. Furthermore, Patent Literature 6 proposes a polymer composition having a carbon nanotube content of 0.25% by mass to 50% by mass, an IZOD impact strength (with notch) of larger than about 2 feet-pound/inch and a volume resistivity of smaller than 1×1011Ω/cm. And it further proposes producing master pellets having a large concentration of carbon nanotubes and adding the master pellets into resin.
However, the carbon nanotubes are dispersed into resin only using mechanical methods, diluting produced masterbatches, thus stable dispersion, or dispersion at a practical state, of the carbon nanotubes into resin has been still yet to be achieved.
Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2001-2915
Patent Literature 2: Japanese Patent Application Laid-Open (JP-A) No. 2002-309101
Patent Literature 3: Japanese Patent Application Laid-Open (JP-A) No. 2002-322366
Patent Literature 4: Japanese Patent Application Laid-Open (JP-A) No. 01-131251
Patent Literature 5: Japanese Patent Application Laid-Open (JP-A) No. 05-503723
Patent Literature 6: Japanese Patent Application Laid-Open (JP-A) No. 08-508534